Process for the separation of hollow glass microspheres from muds containing them

ABSTRACT

Process for recovering at least 70% of hollow glass microspheres having an average diameter, according to the ASTM D1214-1989, ranging from 5 to 200 μm contained in a mixture of drilling mud and cuttings which comprises: a) screening, if necessary, the mixture through one or more 5 to 20 mesh sieves; b) feeding the screened mixture to one or more cyclones and/or hydrocyclones arranged in series, each of which is fed with a volume flow-rate from 1.5 to 10 times higher than the maximum nominal operating value.

[0001] The present invention relates to a process for the separation ofhollow glass microspheres from muds containing them.

[0002] More specifically, the present invention relates to a process forthe separation of hollow glass microspheres contained in muds andcuttings produced during the drilling of oil wells or wells for theproduction of natural gas.

[0003] As it is well known, during the drilling of wells for theproduction of oil or natural gas, particular fluids are used, commonlycalled drilling fluids or muds, whose purpose is of primary importancefor the correct and safe handling of the well preparation phase. Asdescribed, for example, in patent U.S. Pat. No. 3,035,042, drillingfluids have numerous functions: they are used for cooling andlubricating the head of the drilling bit probe; they remove and carry tothe surface the cuttings produced during drilling; they help to seal andconsolidate the well walls; they keep the cuttings in suspension whenthe drilling is momentarily stopped; they contribute to forming ahydrostatic pressure which serves to control and regulate the flowtowards the surface of oil/gas under pressure when the bit reaches thereservoir.

[0004] The most traditionally used drilling fluids consist of aqueous oroily dispersions of clay and/or sandy materials such as bentonite,illite, kaolinite, etc. These are fluids with a thixotropic behaviour,so that when the drilling is stopped, they tend to gelify and preventsedimentation of the cuttings around the bit. Dispersing agents orfluidifying agents can also be added to these fluids to maintain theirviscosity at low values during drilling, to enable them to easilyentrain the cuttings produced by the bit. Examples of dispersing and/orfluidifying agents are lignin sulfonates, lignites, synthetic polymersof (meth)acrylic acid and/or of (meth)acrylamide, etc. Details on thecomposition of drilling fluids or muds can be found in European patent565,187.

[0005] For all drillings in which the normal density of the drillingfluid creates a hydrostatic pressure which exceeds the fracturinggradient (resistance of the rock to hydraulic pressure) of the formationor when the existence of natural fractures in the formation annuls thefracturing gradient, lightened mud is used to reduce the hydrostaticseal in the well. In this way, absorptions and/or damage due to theinvasion of fluids in the formation are limited. Exceeding thefracturing gradient is a problem which arises in particular indeep-water drilling where there is a limited difference between thisgradient and the hydrostatic load required by the drilling fluid forcontrolling the pore pressure of the formation.

[0006] In order to lighten drilling mud, hollow glass microspheres witha low density having an average diameter, measured according to ASTMD1214-1989, ranging from 5 to 200 μm, can be fed, in an intermediateposition of the well. These microspheres reduce the density of the mud,once the larger drilling cuttings have been eliminated, to valuesranging from 0.7 to 1.3 g/cm³, preferably from 0.95 to 1.05 g/cm³. Thesemicrospheres, capable of resisting the strong pressures present insidethe wells, are available on the market as the commercial product ofMinnesota Mining Manufacturing (3M), for example under the trade-name ofS38HS, with an average density ranging from 0.35 to 0.41 g/cm³ and anapparent density ranging from 0.19 to 0.28 g/cm³. In literature, patentU.S. Pat. No. 2,978,340 describes a process for the preparation ofhollow glass microspheres.

[0007] If the use of hollow glass microspheres solves, on one hand, theproblem of the hydrostatic seal, on the other hand, it creates anotherproblem in that it is extremely difficult to separate these bubbles fromthe mud in order to re-use them. As a result, large quantities of thesemicrospheres are lost.

[0008] The Applicants have now found a method which allows the recoveryof at least 70% of the hollow glass microspheres dispersed in a mixtureof muds and cuttings, coming from a drilling well, which is simple as itdoes not require the use of any particular technological expedients.

[0009] The object of the present invention therefore relates to aprocess for recovering at least 70% of hollow glass microspheres havingan average diameter, measured according to ASTM D1214-1989, ranging from5 to 200 μm contained in a mixture of drilling mud and cuttings whichcomprises:

[0010] a) screening, if necessary, the mixture through one or more 5 to20 mesh sieves;

[0011] b) feeding the screened mixture to one or more cyclones and/orhydrocyclones arranged in series, each of which is fed with a volumeflow-rate from 1.5 to 10 times higher than the maximum nominal operatingvalue.

[0012] At the end of the possible screening, a part of the cuttingsproduced by the bit during drilling, higher than 50% by weight, issubstantially eliminated, leaving a fluid which has a density rangingfrom 0.7 to 1.3 g/cm³, preferably from 0.95 to 1.05 g/cm³, and a contentof microspheres ranging from 1 to 30% by weight, generally from 3 to25%. This fluid can be recovered by a high power pump, for example amultistage centrifugal pump, having a specific power equal to at least1.5 kW/m³/h, and fed to the cyclones. There are generally 1 to 3cyclones in series.

[0013] The viscosity of the fluid, which depends on the type of well inwhich it is used, can be regulated to optimum pumping values by dilutingthe mud or thickening it with clay and/or other viscosizing agents.

[0014] The cyclones and/or hydrocyclones used in the process object ofthe present invention are traditional devices described, for example, in“Ullmann's Encyclopedia of Industrial Chemistry”, Fifth Edition, 1988,Vol. B2 or in “Hydrocyclones”, L. Svarovsky Holt, Rinehart and Winston,1984, and are capable of treating dispersions and/or suspensions ofsolids with nominal operating flow-rates ranging from 3 to 30 m³/h.

[0015] The cyclones and/or hydrocyclones, also commonly called cycloneseparators, are generally dimensioned so as to guarantee a flow leavingthe base, rich in heavy solids (underflow, UF) and a counter-flowleaving the head, rich in light fraction (overflow, OF). In the processobject of the present invention, the overflow leaving the first cyclonecan be fed in turn to one or more cyclones in series, operating underanalogous conditions to the first, if a forced separation of themicrospheres from the mud is necessary. In any case, operating eitherwith a single cyclone or with several cyclones arranged in series, arecovery of hollow glass microspheres in the overflow equal to at least70% of the microspheres fed and even over 80%, can be obtained. Thisstream can be re-used as such and fed to the well to lighten thedrilling mud or it can be subjected to further treatment, for example bysedimentation/flotation in water or another liquid, to recover thesubstantially mud-free microspheres.

[0016] Two illustrative and non-limiting examples are provided for abetter understanding of the present invention and for its embodiment.

EXAMPLE 1

[0017] An amount of mud was prepared in a 10 m³ tank, having thefollowing composition: Products Quantity (kg) weight % Water 4000 64.0KCl  150 2.4 Starch  50 0.8 Xantanes  25 0.4 Antibacterial agent   6 0.1Cuttings 1439 23.0 S38HS Microspheres (3M)  579 9.3 Total 6250 100.0

[0018] The density of the mud was 0.927 g/cm³ which, by dilution, wasregulated to 0.956 g/cm³.

[0019] The mud was fed, by means of a pump having a power of 90 kW, to acyclone with flow-rates of 38 and 60 m³/h. The maximum nominal operatingflow-rate of the cyclone was 21 m³/h.

[0020] A stream of fluid (OF) in which the microspheres areconcentrated, is recovered from the head of the cyclone, whereas thecuttings are concentrated in the stream at the bottom (UF). The resultsobtained are indicated in Table 1. TABLE 1 Flow-rate fed Recovery of(Inlet) Flow-rate OF OF/Inlet microspheres (m³/h) (m³/h) (%) (%) 38 1026 70 13 34 74 60 16 27 77 19 32 81

EXAMPLE 2

[0021] Mud prepared and diluted as in example 1, was used for running atest with two cyclones in series with a maximum nominal flow-rate of 11m³/h and 21 m³/h respectively, the second cyclone being fed with the OFof the first. The UF of the first cyclone was regulated so as to formabout 13% of the flow-rate of the flow-rate of the fluid fed. The powerof the pump was 90 kW. The results obtained are indicated in Table 2.TABLE 2 Flow-rate fed Recovery of (Inlet) Flow-rate OF OF/Inletmicrospheres (m³/h) (m³/h) (%) (%) 55 14 56 76 18 33 79

1. A process for recovering at least 70% of hollow glass microsphereshaving an average diameter, according to ASTM D1214-1989, ranging from 5to 200 μm contained in a mixture of drilling mud and cuttings whichcomprises: a) screening, if necessary, the mixture through one or more 5to 20 mesh sieves; b) feeding the screened mixture to one or morecyclones and/or hydrocyclones arranged in series, each of which is fedwith a volume flow-rate from 1.5 to 10 times higher than the maximumnominal operating value to obtain an underflow rich in heavy solids andan overflow rich in light fraction.
 2. The process according to claim 1,wherein the overall mixture, after screening, has a density ranging from0.7 to 1.3 g/cm³ and a content of microspheres ranging from 1 to 30% byweight.
 3. The process according to claim 1 or 2, wherein the overflowis subjected to sedimentation/flotation in water or another liquid, torecover the substantially mud-free microspheres.
 4. The processaccording to claim 1, 2 or 3, wherein there are from 1 to threecyclones.
 5. The process according to any of the previous claims,wherein the cyclones have nominal operating flow-rates ranging from 3 to30 m³/h.